Electrochemical deposition (i.e., electrochemical plating or electroplating) uses electrical current to coat a conductive object with a layer of metal. The surface to be plated (i.e., the working electrode) is submersed in an electrolyte containing salts of the metal to be deposited. The surface to be plated may connected to a current source in such as way as to be a cathode, for example. Another electrode (i.e., the counter electrode), which is connected to the current source so as to be the anode, for example, is also immersed in the electrolyte to create an electrical path. For example, to deposit a layer of copper on a conductive wafer, the wafer may be submersed into an electrolyte containing copper salts along with a sacrificial copper conductive electrode. A current source is attached to the wafer and the electrode to perform the electrochemical deposition.
After the wafer is submersed in the electrolyte, a potential is applied between the wafer and the electrode. For example, the wafer may be the cathode, while the other electrode is a anode. Current flows between the anode and the cathode, causing metal from the electrolyte to deposit on the cathode (the wafer). The metal at the anode is oxidized from the zero valence state to form cations with a positive charge. The cations associate with anions in the solution. The cations are reduced at the cathode (i.e., the wafer) to deposit in the metallic, zero valence state. For example, using a copper counter electrode in a sulfuric acid electrolyte, copper is oxidized at the counter electrode to a Cu2+ cation. The Cu2+ cations associate with SO42− anions in the electrolyte to form copper sulfate (CuSO4). At the cathode, the Cu2+ cations are reduced to metallic copper. In this way, a layer of copper can be deposited on the wafer. The thickness, consistency, density, resistivity, and other characteristics of the deposited copper layer depend on the process conditions used to deposit the layer. Devices for evaluating several electrochemical reactions have been implemented. These devices include a working electrode that is a cylindrical metal rod. Several of these working electrodes are plated simultaneously for later evaluation.
Thus, what are needed are new techniques for testing various electrochemical deposition processing conditions for semiconductor processing.